Coded track circuit signaling system



July 2, 1946. N. D. PRESTON CODED TRACK CIRCUIT SIGNLNG SYSTEM File@ June 3o, 1944 5 sheets-sheet 1 Snveutor,

2, 1946. f N. D. PRESTON CODED TRACK CIRCUIT SIGNALING SYSTEM 5 Sheets-Sheet 2 't Filed June 30, 1944i Bnventor July 2, 1946. N. D. PRESTON I "CODED TRACK CIRCUIT SIGNALINCLSYSTEM `Filed June 30, 1944 3 Sheets-Sheet 3 kmmxww El LK S IT .mfom

. RG n Stwentor WMM- AIIIII Patented July 2, 1946 i UNITED j STATES Y PATENT? oFFic' ooDEn'TaAcK CIRCUITISIGNALING- Y. SYSTEM f Neil D. Preston, Rochester, N.: Y., assigner to General' Railway Signal Company, "Rochester,

l Application June 30, 1944, Serial No. `542,909

lClaims.

This'invention relates to coded track circuit signaling systems for railways, and more particularly to a coded track circuit organization employing code pulses of different polarity andernbodying suitable means for preventing false signal'indications in the event `ofy a failure of the insulated joints at the signal locations.

In certain applications of coded track circuits to the control of automatic block signalsand` the like, it becomes expedient to employ code receiv-j ing means responsive to code'pulses of different polarity. For instance, in the interests of obtaining more uniform decoding response under variable ballast conditions, for better shunting, and for other purposes, it is desirable to' employ code pulses of alternate polarity at different time spaced intervals for operating a magnetic stick type of code following track relay 'atdifferent code rates for different signal indications, as dis- Vclosed for example in the 'prior applicationv of F. X. Rees, Ser. No; 466,151, flled November 19,

'ferent polarity to the track rails of the rear track Asection on the opposite side of the insulated joints, it can be appreciated that a failure of these insulated joints will render the code pulses applied to the rear track section effective to operate the track relay means for theforward track section; and under certain conditions may cause a false coding operation of this track relay Ameans which will result in the display of an improper indication of the associated signal. In other words, where the signal indications are governed by code pulses of different polarities, broken down insulated joints may cause dangerous false clear signal indications.

The primary object of this invention is to provide simple and effective means for preventing.

such improper signal indications in such a polarized coded track circuit organization in the event ofthe failure of the insulated joints at a signal location. i Y

Generally speaking, and without attempting to define the nature and scope of the invention,'

protection against false signal indications in the event of a failure of the insulated joints associated with a signal is vobtained by rendering the 'code pulses appliedrto the rear track section ineffective to operate the code following track relay v pulse is being 'applied tothe rear track section,

so that the signal cannot be improperly cleared by the code Apulses from the rear track section, in spite of a failure' "of the'insulated joints, and i remains'- at stop until legitimate signal control pulses are received, whereupon the code following track relay 'is connected' directly to the forward track section independently of the application of code pulses to the rear track section, and may be operated at any desired `code rate without interference. y 1 v i In a coded track circuit'organization of this character, it may be expedient tov provide inverse or off4 code pulses for approach lighting the signalv o'r for otherjpurposes; andprovision is also made in accordance" with this invention to afford broken down joint protection when such an inverse code iis used.' More specifically, itis 'proposed that the inverse code pulses shall all be` of the same polarity, and since the code following track relay of the adjacent section requires v,opposite polarities alternately to effectively operdesired `broken down joint Aprotection for normal train movements; `but when a clear indication of a signalshould be changed to caution or stop by removal of the legitimate signal controlv pulses without shuntingr the code following track relay,

Vas in the `case of a back-up train movement, or

operation of an outlying switchinanother track section, then the clear indication of thesignal may be maintained under broken down joint conditions atleast until aftrain approaching that signal puts it to stop by its shunting actionacting past the broken down insulated joints. Accord- Yingly, it is proposed in accordance with this lnvention `to employrv different coderates for the clear indication in,adjoiningtrack sections adjacent eachgsigna'l, so ,that code` pulses applied to the track section ,in the rearof a signal cannot 'give a clear indication of that signal under broken "down joint conditions, because suclr code pulses are not of the'proper rate. With such an ar- Y rangement of diierent 't In the accompanying drawings, j

3 clear code ratesfor alternate blocks, whenever the legitimatev clear code pulses for a signal are cutro, this signal will give t y Athe proper restrictive indication.

Various other` objects, attributes, operating characteristics Yand advantages of the invention will bein partapparent, and in part pointed out as the'specinc embodiment of vthe.;inver'ition;are later described; x1

Fig. l illustrates in `a diagrammatic and con- -n ventional manner a stretch of track for; a1 multiple;

track railroad equipped with block signals havingtheir indications governed in accordance with the Y. rate ofV code pulses of different polarity, and provided with broken down joint protectiveV means inaccordance with-this invention;

Fig.- 2 is an explanatory diagram illustrating the general nature of the signal control codes ein ployed in the organization of Fig. 1; Y 1

Y Figs. 3A and 3B, when arranged end to end, illustrate the same .type of system shown in Fig.` l, with vinverse or oil code-pulses for approach lightingcontrol; and

Figs. 4A andAB are explanatory diagrams ilafioaizo Y 4 eration of thistrack relay. Another secondary I5 of the decoding transformer I3 is connected by a ,Y tuned circuit and full-wave rectier I6 toa slow- ""spon'se' to a coding'operation of the track relay Y release distant relay'l), in accordance with ther `I kwell known practice. This arrangement of code responsive means, which is merely Vtypical of .anV

organization suitable for this Vpurpose and which maytake otherforms, operates in the well known c 'manner fainiliarV to those skilled in` the art toY maintain energization of the home relayLH in re- 'Z'I'Rat any/of the selected rates, but to maintain nergization of the distance relay 2D only when the track relay ETR is operated at some particular clear code rate for which the tuned circuit and decoding equipment is constructed or adjusted.

lustratinghthe signal c ontrol andv inverse code pulses employed in the organization of Figs. 3A and 3B. Y

The illustration of the electrical circuits in the v accompanying drawings has been simplified by indicating by arrows and gthe symbols (-I) and (-)v connections to the opposite terminals of batteries or other suitable sources of current; and in general, the parts and circuits have been shown in these drawings in the conventional manner, more with the view of facilitating an explanation and understanding of the operating characteristics and functions of thek invention, thanv for the purpose of showing in detail the particular struc-` 'On'e specificembodimeiitof the invention is illustrated in' Fig'. 1. in connection with 'the control Y of conventional three-aspect'jautomatic block sig- 'rials Zand 3 fora multiple vtrack railroad by code tures and arrangements of parts preferably em- Y40 ployed in 'practice pulses of alternate polarity of die'rent clear and caution code rates. Forsimplicity, it has been assumed that each block between successive signals comprises onetracksectio'n; but it'jsh'ould be Vunderstood that suitable cut sections, with means for relaying or repeating the code, may be employed. The normal direction of traic is from left to right. Y

'Referring to the relays and circuits associated with the signal 2 inFig. 1 as typical ofthe apparat'usv at each signal location, the codel following track relay ETR is a two-position polar ray of the magnetic stick type having no spring bias, and acts to operate and hold its armature and contact fingers illustrated conventionally in one extreme' .position or the other in 'response to the momentary energization of its energizing circuit with :one or the other .polarity ofrcurrent. This relay ,is preferably constructed in accordance with recognized practice to be quick acting, and thus re'- 4sponds to current pulses of short duration. The operation of the contact finger I2 of this track vrrelay ZTR governs the energization ofthe two halvesy of the primary of a decoding transformer |3, one secondary of which is connected to -a Slow,-v -reslease home relay 2H ythrough the contactsfof another contact finger I4. of this track relayperforming the functionsof rectifying contacts Vto VVcause energization of this relay 2H by uni-direcgtional currentV pulses in response to Vthe codingop- For reasons explained more fully hereinafter, the

f distant relay 2D for the signal 2 requires for its energization one particular clear code rate, such as 180 cycles per minute, while the distant relay 3D for the signal 3 next in advance, and likewise the Vdistant relay for the lsignal (not show'nin the rear of signal 2 requires for its energization a different clear code rate, such as ,code cycles per minute. i g f1 The signal 2 may bejof any suitable typegoverned in accordance with recognized practice by the home and 'distant relays 2H and 2D so as to indicate clear when both relays 2H and 2Dare en- Vnal indications, a transmitter relay 2CTP is arranged to be connected through front and back contacts I9 respectively of thehome relay 2HV by ,obvious 'circuits toY coding contacts operating atk 'the clear and caution code rates, assumed to be ,120 and 75 times per minute in the case of signal 2. by suitatble code oscillators lor motor operated Acoders shown diagrainmatically and designated Iu'CT and 15CT.

" Transmitter relay 2CTP operates the armature ,and contacts of a repeater or chopper relay 2XCT to diire'nt positions as the transmitter relay is `ei'iergized'and deenerg'ized; In the specific ,ar-

rangement illustrated, this chopper relay ZXCT is Pa two-position polarized relay of the magnetic stick type Without any `gravity Ior spring biasand is provided with two windings respectively ener- -g'i'zed through front and back contacts 20 of the transmitter rel-ay ZCTP. The energization of the lower winding of this chopper relay ZXCT is assumed to vcause movement of its contact fingers vto the left-hand position as shown, and the energization of the other winding moves the contact fingers to the other-dotted lineposition. The trackr battery IB 'for the track vsection IT in 'the rear of signal 2 is connected through resistor IR and through front and back contacts 2I and 22 of the transmitter relay'ZCTP, which act as pole vchanging contacts, in series with contacts closed in Atheor'iposite positions of the contact fingers 23 and 24 of ythechopper relay ZXCT, in a manner to .provide pulses of opposite polarity as the trans- Vmitter relay 2CTP is energized and deenergized at the code rate then eiiectivasuch code pulses hav-f aai-,fsa

ing a relatively short duration corresponding with rthe' operating time of the 'chopper relay 2XCT..` Considering now the provision made for broken down joint protection, the code following track relay 2TR for the forward track section 2T in advance of signal 2 is connected to the track rails of this track section by circuit connections including front and back contacts 25 of the transmitter relay 2CTP and contacts closed with the contact finger 26 of the chopper relay 2XCT in corresponding extreme positions, so that while the transmitter relay 2CTP andthe chopper relay 2XCT are momentarily out of vcorresponding positions during the time interval the track battery IB is connected to the rear track section IT, the track relay 2TR. is isolated or disconnected. For example, withl the transmitter relay 2CTP and the chopper relay 2XCT in the position shown in Fig. l subsequent to the transmission of a code pulse of one polarity (assumed to be positive), and with the track battery IB disconnected from the rear track section IT, the track relay 2TR is connected across the track rails of the forward track section 2T through the back contact 25 of the transmitter relay 2CTP and a contact finger 26 of the chopper relay 2XCT in the lefthand position. As soon as the transmitter relay 2CTP is energized to apply the next code pulse of opposite polarity to the rear tracksection IT, its back contact 25 opens the circuit connections for the track relay 2TR, and isolates this track relay, so to speak, until the chopper relay 2XCT has operated to cut 01T the track battery IB by movement of its contact fingers to the dotted line position, whereupon track relay 2TH. is again connected to its track section through the front contact 25 of the transmitter relay 2CTP and the contact finger 26 of the chopper relay 2XCT in the dotted line position.

In short, during each of theti'zne intervals that the track battery IB is connected to the rear track section IT, the track relay 2TR is disconnected from the forward track section 2T by the operation of the contacts 25 and 26 of the relays 2CTP and 2XCT, so that in spite of any failure ofthe insulated joints, code pulses applied to the rear track section IT cannot operate the track relay 2TR under such conditions.

.These contacts 25 and 26 of the transmitter relay 2CTP and the chopper relay 2XCT are shunted by a front contact 21 of the distant relay 2D; and consequently, when this distant relay 2D is energized, code following track relay 2TR is connected directly to the track section 2T, and may be operated at :any desired code rate independently of code pulses applied to the rear track section IT.

A block signal system using signalcontrol codes of alternate `polarity .at different codev rates, as diagrammatically illustrated in Fig. 2, operates to govern the signal indications in the same generall manner as the usual rate code system. Under normal conditions and with no trains present, the code pulses of alternate polarity transmitted over the track rails in each block are spaced at time intervals corresponding with the clear code rate, which is preferably the same for every other block and different for adjacent blocks; and the coding operation of the code following track relay of ,each signal, such as the track relay 2TH., at the clear` code rate energizes the home anddistant relays 2H and 2D to cause the associated signal 2 to indicate clear.

Assuming 'now that a trainlpasses signal '2 under. these normal conditions, the .s'huritingg ac n tion voi? @the .wheels and axles of this train stops the coding operation of the track relay ZTR,

leaving its contact fingers I2 and I4 in thelastV operated position; and consequently, thehome relay 2H and lthedistant relay 2D both release to cause the signal 2 to indicate stop. Under these conditions, with the front contact 21 ofthe distant relay 2D open, the track relay 2TR is disconnected or isolated during the time intervals, when code pulses are applied to the rear track section IT, by the operation of the contacts 25 and 26 of the transmitter relay 2CTP and the chopper relay 2XCT.

Assume now that the insulated joints at signal 2 are broken down by the movement of this train, and that the wheel shunt of the train in question is removed While the train still occupies the block protected by the signal 2, as for example, because the train has advanced beyond the insulated joints at a cut section or beyond a point where v by giving a false clear indication for the signal 2.

If the Wheel shunt is removed because the train advances out of the block 2T past the signal 3, the failure of the insulated joints may give an improper clear indication for signal 2 instead of the proper caution indication, particularly if legitimate caution code pulses are not transmitted toward the signal 2 on account of'some failure of decoding equipment.

In accordance with this invention, however, such improper coding operation of the track relay due to a failure of the insulated joints cannot occur, because the track relay is isolated at the time code pulses are applied to the rear track section,` and-will be energized only by legitimate code pulses received over its own track section.

In this connection, it should perhaps be pointed out that under broken down joint conditions at signal 2, for example, the Wheel shunt of vany following train approaching this signal is likely to stop coding operation of the track relay 2THl and putAthe signal 2 tofstop before the train Y'reaches it;` but va clear indication of signal 2 at the entrance to an occupied block, or at the entrance to a block next in the rear of an occupied block, Which may occur under broken down joint conditions Without protective features of this invention, represents an unsafe condition, which is not obviated merely because the train puts the signal to stop in its face. This is :because a train is not provided with a safe braking distance from such a stop signal to the hazard ahead. Thus, for reasons oi safety it is necessary that a caution signal indication be given at the signal next in rear of a stop signal, regardless of the cause for which such signal is at stop.

Assuming normal operating conditions, when the train in question passes signal 3 out of the block 2T protected by the signal 2, and 1egitimate caution code pulses are transmitted toward the signal 2, the track relay 2TH, is energized as soon as one ofvthese legitimate code pulses is out of step, so to speak, with the operation of the transmitter relay 2CTP Aand the chopper relay 2XCT,

, so as to existduring the time in which code'pulses are not being applied to the rear track lsection ITfand-track relayi'lIFt` is effectively 'connected thougn these legitimate caution code pulsesjin theiorwardtrack section 2T arecreatedby co'ding contacts nominally operatingat the. same Vcauti'c'i'n code rate asl vthe codingcontacts. 'ISCT governing tnetransmitter relay ZCTP, on account v,01 unavoidable variations in manufacture or adjustment, these different coding contactsV Willnot V` continue to open and close at precisely the same instant for any substantialfl'ength of tim'aeven though these contacts should happen vto loeV operatingsynchronously at the instant that the AWheel shunt is removed. Further, since the code pulses employed with this invention are relatively short` as compared with the time'spacing between them, as'indicat'ed roughly in diagrams oi' Fig. 2;

mate code Ypulses are Ymomentarily applied to the track section 2T twice for each interval at the cautionV 75 coderate, or'lrOper minute. The net resultis. what may be termed a beat code condition, under which the track relay ZTRYis' intermittently energized at recurrent intervals at the caution code rate, with one code pulse occasionally blanked out because it occurs at the time this track relay is isolated. Such intermittent operation of the track relay 2TR is sufficient to maintain the home relay 2H energized, this'relay having the usual slow releasing characteristic and being sufciently long in its release time to maintain its armature in the attracted position fork the blank intervals in the regular coding operation oi the track relay 2TR at the caution code rate. l

Thus, under normal operating conditions and where legitimate caution code pulses are transmitted at signal 2, the home relay 2H is energized to cause the signal to indicate caution; :but the contacts 25 and 26 of the transmitter relay ICTP when code pulses at the I 20 caution 'code Vrate v are applied to the rear track section IT. Conse- I quently, even if the insulated joints at the signal Vrear track section IT;

2 should be broken down, improper coding operation of the track relay 2TR at the clear codek rate and an improper clear indicationl of the signal 2 cannot be caused by codel pulses forfthe Vrear track section IT, either alone orV in combination with the legitimate caution code pulses in a 'codefor block-2T is at the 180 code rate different from the 120 'code rate forrthe clear code for the '58 Y and hence for the reasons previously considered, therev will be intermittent operation Vo'fithetrack relayiZTR byla'numberof pulses at the clear 180 code.v rate without intere ference bythe v'operation ofthe; transmitter relay QCTP Vand thev `chopper relayQXCT. This energizes thedistant yrelay 2D, whereupon'the front Vcontact 2T of thisflrelay closes t0 connect the track relayl 2TR Ldirectly to thetrack section 2T or Where an outlying switchiisinvolvcd, `loy removal of the normal legitimate codes., "For this reason, in thepreferred embodiment of the invennen umstrated, different clear code rates are employed for adjoining blocks, with the same clear code used in every other block. vWithjthis arrangement, if the legitimate- 180 clear codeffor track section 2T governing the signal 2, for example, should be removed in connection with' a back-up tranmovement or/by operation 0f a switch or thelikaas distinctivejfrom an effective wheel shunt in track section 2,' thefdistant' relay 2D is automatically deenergized, regardless of broken down joint conditions, because this distantirelay 2D requires for its energiz'ation a cod-` ing operation of the track relay 2TR at. the .180 rate; and the code pulses applied to 'the rear track' sectionV IT are 'at adifierent120fcodevrate.

This deenergiza'tionfof the distant relay 2Dand the openingv of itsfrontjcontact 2l' renderszth'e contacts 25 and 2t of the'tian'smitter,re1ay'.2CTP and the chopper relay ZXCTeffective'to cutr voff or isolate the track relay 2TR at the particular times any code pulses areV applied to' the rear track section IT. Therefore, if all'legitimate code pulses toward the signal 2 are out ofi, thefcoding operation Aof the track relay 'IRceases .andl'the home relay 2H, aswell as the distant relayLZD releases, putting signal 2 Vto stopand changing the code rate Yforthe vrear track' sectionIT'to the f proper caution indication Vfor the signal (not shown) in the rear 'of signal 2. If, however, legil timate caution` code pulses are being transmitted toward signal 2', thenthe home relay 2H ismaintained energized under beat code conditions',- and thensignall gives the proper ycaution indication.

Thus, with diierent clear code rates in every other block in accordance with' the preferred embodiment of the invention, any removal or change in the rate of legitimate signal control codes transmitted under normal clear ,conditions will govern the signals accordingly, in spite of any failure'of the insulated joints.

Inthe foregoing discussion, the protective fea` tures forb'roken down insulated joints have been `discussed in 4connection with train movements, v.

since if no trains are present, thefindications of the signals are-'not essential from the standpoint of protecting trac. 'Insulated joints,however, may forv some reason deteriorate and fail under normal coding,conditionswith'ou-t any trainmovement, and while the indications-displayed by a signal'under such circumstances is ynot material, it may be pointed out that the track relay 2TR, for example, is in effect under such conditions subjected to short code pulses of alternate polarity at different code rates supplied by different coding contacts and transmitter relays 2CTP and 3C'IP. Generally speaking, the combination of short code pulses of alternate polarity at both 120 and 180 code rates, tends to produce a variable coding operation of the track relay 2TR, which is likely to Ycause the distant relay 2D to release, dependent upon its slow releasing characteristics, the general eiTect of the code combination in question being to operate the track relay temporarily first at the 120 rate and then at the 180 rate. If the distant relay 2D should release under these conditions, the opening of its front contact 2l isolates the track relay 2TR from the influence of the code pulses for the rear track section T, leaving ther code pulses in the forward track section 2T eiTective to govern the relay 2D without interference. The resultant energization of the relay 2D and closure of its contact 21 again renders the track relay 2TH. subject to combined eiiect of the 120 and 180 codes, thereby again releasing relay 2D. In other words, dependent upon the operating characteristics of the various relays and other conditions, a failure of the insulated joints under normal coding conditions without any train movement will ordinarily result in an intermittent change or pumping action betweenclear and caution indications of the signal. Such erratic operation of the signal, while of no significance from the standpoint of protecting train movements, attracts the attention of the engineers of passing trains to the abnormal conditions. In this connection, however, the failure of insulated joints are effectively detected or betrayed under ordinary circumstances, because the train approaching the signal puts it to stop in Yits face.

A coded track circuit of thetype contemplated, which employs relatively short pulses of alternate polarity, provides a regular coding operation of the track relay independentv of variations in battery voltage, ballast resistance and the like, since the back and forth movement of the armature of the track relay is determined by the time spacing of the code pulses, and is not materially affected by the degree of energization of the track relay under different ballast conditions and battery voltage. Also, the relatively short pulses are necessarily of a, higher peak voltage than if maintained for a longer time interval, and tend to break down the resistance of any film on the trackway and give better shunting performance. Further, a polar relay of the magnetic stick type without any spring b-ias can generally be arranged to have greater sensitivity than a biased polar `track relay, so that operating energy may lI f be transmitted with less losses over longer track circuits.

Broken down joint protection for inverse codes-In connection with the approach lighting of signals, control of the protective devices at highway crossings, and for similar purposes, it is sometimes desirable to provide what is conveniently termed inverse or oli code pulses in conjunction with the signal .controlling driven codepulse's; and in the type of coded track cir; :y

cuit contemplated, it is` advantageous to employ relatively short pulses for such inverse or 01T codo control. 'lf such inverse code pulses of alternate polarity are employed,` and are of sui.

at the end of a track section in the. rear of a signal, it can be appreciated that, if the insulated joints at such signals should be broken down,-

such inverse code pulses are likely to cause a coding operation of the code following track relay governing the signal, thereby under certain conditions giving the improper signal indication. Figs. 3A and 3B illustrate the same. arrange-vv ment shown in Fig. 1, supplemented by code transmitting and receiving means for inverse code pulses for approach lighting control, to. gether with protection against broken down insulated joints in accordance with this invention for such an organization. y f Referring to the apparatus at signal location 3 in Fig. 3B as typical of the various signal 1ocationsl of this modied form of the invention, it will be seen that the same apparatus is provided as in Fig. 1, with the addition of certain means which is employed in connection with the transmission and reception of inverse codes. The track relay STR is associated with the track section 3T and is isolated therefrom by the front and back contacts |00 and |0| of relay SCTP and 3XCT, when these contacts are out of corresponding positions in the same manner as previously described. II'he front contact |02 of re lay 3D is similarly employed to shunt the isolata ing, contacts IDU and IUI. However, the track relay 3TR is normally connected to the track rails of the section 3T through a contact |03 of inverse code timing relay' 3AXCT and a front or back contact |04 of an inverse code transmitting relay SATCP. Whenever a driven code pulse is received of a particular polarity, it causes, the transmission of a momentary inverse code pulse through the proper control of the inversecode transmitting relay SACTP and associated timing relay SAXCT which Vis controlled by front and back contacts |05 of relay 3ACTP. Y

At the leaving end of the rear track section 2T, the code transmitting relay SCTP and its as-` sociated timing relay 3XCT operate toput driven code pulses on the track section 2T in the same manner as described in connection with Fig. 1, but in addition to such apparatus, an inverse code receiving track relay ZA'IR of the two-position magnetic stick type is employed so as to .be operated to one position'by the reception ofl an inverse code pulse, and to be operated to the opposite position in accordance with the transmission oi' the Ifollowing driven code pulse. This and 2ABP which are neutral relays with slightly slow releasing characteristics, so as to be maintained picked up between successive energiza-V tions as the result of the operation of relay ZATR responsive to the reception of inverse code pulses.

The green, yellow and red lamps of the .signal 3 are controlled in accordance with the position of the home and distant relays 3H and 3D the sameas in Fig. l,` but these lamps are illuminated only when a train approaches the signal 3 and deenergizes the relay 2ABP. This is effected by including back contact |06 of relay ZABP in the energizing circuits for these lamps, it being understood that normally` inverse code is being received so that back contact |08 is normally opened.

Let us now assume normal conditions and con- Sider how `driven and inverse codes areI transmitted through the track section 2T. Assuming that a driven code of the code rate is being ifi tainithrough its front contact H12 a circuit connection for the track relayl TRtothe track section 3T independently ofthe operation of the 1 1 transmitter relay V3CTP and. its repeater relay SXCT supplying driven code pulses to the rear track section 2T, so that the track relay 3TH may fol-low the code inthe forward track section ,3T without interference.

Considering the operation beginning at the particular time when the contacts of the `coder I80CT next close to energize the' transmitter relay SCTP, as indicated by the line a-'-a vin the diagram ofY Fig. 4A,a driven code pulse is encargo applied toA the rear track section 2T from the v track battery 2B through a series limiting resistancel 2R', front contacts 01 and |08 of transmitter relay 3CTP, and polar` contacts vIll'and IIU ,of the relay SXCT in the left-.hand position shown.V At the same time, the front contacts Hi8 and II 2 of the transmitter relay SCTP vact to connect the inverse code following track. re-

lay ZATRl across a selected portion of the'limting resistance 2R, so that the'voltagedrop4 caused by the driven code pulse supplies a momentary energizing current for the inverse code track relay ZATR to restore its Vcontact H3 to the right-hand dotted line position. This restoring rcircuit connection for the relay 2ATR may traced from theV left-hand side of the resi'stoz'l 2R, front contact IUS of relayY SCTP to right-hand Side of track relayV Z'ATR, winding of this track relay and Vfrontcont'act H2 of relay 3CTP to the adjustable connection to the' iesistor'r 2R. Also, the energization of the transmitterV relay 3CTP closes itsY front contact II I to energize the `upper winding of relay SXCT and shifts its polar contacts |09 and'II to the right and terminate the' drivenv code pulse in the 'same manner previously discussed. Y

Referring now to Fig. 3A, the reception of this driven code vpulse at the other end of the track section 2Tenergizes the code following track re- Y lay 2TRWhich at the time under consideration is connected tothe track section 2T through a front contact. 21 of the distant relay 12D, polar Vcontact II 5x04? relay ZAXCTV to the right and f front contact H4 of inverse code transmitter rc-Y Vlay 2ACTP. With the arrangement of circuit connections and p'olafrities assumed for the particular organizationillustrated, the driven code pulse under consideration shifts the polarcontact I2 of the track relay ETR from the position shown to the left, and opens the circuit then closed andv of its associated coding contacts IBIICT, corre-V sponding with what may be termed the beginning of the on period of a driven code. When the coding contacts ISEICT open and the transmitterrelay SCTP in Fig. 3B is deenergized, a driven code pulse of the other polarityis applied to the track rail track'section 2T through back contacts I'Il'l, IilV of this transmitter relay until the polar contacts His and VI l0 of the relay BXCT are shifted back to the position shown by energization of the lower winding of this relay 3XCT. At this .time the front contact II2 of the transmitter relay BCT? is open and disconnects the resistor 2R from the inverse code track relay Z'ATRf, so that the driven code pulse of this other polarity does not affect the inverse code track relay. However, when this` driven code pulse ceases and the polar contacts H0 and I I9'of the relay XCT assume the left-hand position, the inverse code following track relay ATR is connected across the track rails of the [track section 2T ready to respond to any succeeding inverse code pulse.

The reception of this driven code pulse at the signal 2 energizes the track relay 2TR through back contact I i4 and front contact 2l so `that its contacts are again operated to the right. The

closure of contact I2 in aright-hand position again energizes the relay ZACTP so that the upf per winding of the relay ZAXCT is energized through front contact IIS of relay 2-ACTP. This causes Contact I I5 of relay ZAXCT to be operated to the right, but during this time of response of Y vthe contact IIS, a ycircuit has'been made to connect the battery ZBB momentarily across the track section 2T 'through front Contact IM of relay 2ACTP'.

Such inverse code pulse applied to the track section 2T obviously occurs following the reception of the driven, code pulse actuating the track relay ETR, and since the driven code pulse has ceased, back contact IIZ of relayV SCTP is closed n and polar contacts I I9 and I Il) of relay SXCT are readily traced on the drawings forenergizing the ,Y

inverse code transmitter relay ZACTP. 4The deenergization of this relayl 2ACTP and opera-tion of its front Contact I I8 causes energization of the the'loattery ZlllBis` noi-connected to lthetrack rails .to providezan inverse-code pulse.

In other Words, a driven codeipulseof one par-` ticular polarity, corresponding withthat associated with the energization of thedriven code transmitter relay by closure of its Vcoding contactsin. the ,particular arrangement shown, prepares' a circuit connection for the inverse code' reception of the inverse code pulses', which are' always 'of the same polarity and which follow the succeeding driven code pulse oi the opposite polarity, causes the actuation of the relay 2ATR; to its other Vor left-hand position. Thus, an inverse code pulse is transmitted during alternate time space periods between the driven code pulses for actuating Ithe inverse code track relay ZATR, which isrestored by a local circuit toa different rposition' during the other time space VVperiods. This continuedlback andV forth operation o'f the contact nger I I3V of the invers code track relay ZATR obviously causes the relay Z'AFP to be picked up to close its front contact I2ily and Vallow the approach control relay'. ZABP to also be picked up. Y y

Although this operation specifically describes the transmission of an inverse code during the presence of a driven code of the 180 code rate 1n the track section 2T, it is to `be understood that a similar operation occursduring the transm1ssion of driven codes of the "l code rate. These two different conditions have been indicated in the diagramsofFigseA and 4B to show the relative operations of the code transmitting relays and the transmission of the inverse code pulses with respect to the driven code pulses. Although the 1Z0 code rate has not been indicated in the diagram of Fig'. 4A, it is to bev understood tliata similar operation occurs in the track sections IT and 3T andother similar track sections where a different clear code rate of 120 is preferably used. Y

When a train enters the track section 2T, further transmission of the'inverse code pulsesin the manner above described ceases, and the contact finger ||3 of the track'relay 2ATR stays in the dotted line] position to which it is restored by the intermittent energization of the transmitter relay 3CTP and continued application of driven code pulses to the track section 2T ahead of the train in'question. vThe energizing circuit for the approach relay 2ABP is thus maintained open, instead of intermittently closed; and after a suitable release time sumcient to span the time intervals Anormally intervening between the successive driven code pulses, the back Contact |06 of this approach relay 2ABP closesv to provide approach lighting of the'signal 3 in the wellknown way.

`The lapproach control aiforded by inverse codes and shown as employed for approach lighting in the particular organization illustrated, may also be used for approach locking and other purposes; and'inthe interests' ofchecking against failure of the restoring circuit, thegrelay 2AFP governing at its front contact |20 the, energizing circuit for the approach control relay 2AB P,. is preferably employed as shown, so that the approach controlV relay 2ABP will be deenergized,'regardless of the particular position in which the contact nger I 3 of the track relay ZATR may happen tostop.

In connection withl certain applications of inverse code for approach control purposes, the inverse code transmission in a track section is discontinued by suitable controk as distinctive from the shuntingaction of a train in such track section; and it is important that there should be no false self-coding operation of the inverse code following track relay due to the presence of a stray potential. Accordingly, in the .organization of this invention, ,the polaritiesv `forthe ,driven and inverse code pulses are preferably chosen as indicated, so as to `provide for 'thesamepolarity of energization of the track 'railsfb'y aninverse code pulse as for the particular driven code pulse reduce theflow 4of current through the resistor` 2R andprevent restoration of said relay ZATR to its other Jright-hand position. Accordingly, the y contact finger ||3 of` the relay2ATR. would stay yapproach control relay 2ABP.

As above mentioned, each track relay, suchas track relay` BTB, in Fig. 3B, for example, is isolated during the transmission of each driven code pulse in the next adjacent track section to the rear while the front contact |02 of the distant relay 3D is open. In other words, the track relay STR is protected against the. false operation from driven code pulsesin'the rear track section 2T the same as explainedin connection with Fig. 1.

It will be appreciated that the track relay 3I'R must be operated tov opposite positions alternately in order to effect any operation of its associated decoding apparatus. Althoughthe inverse code pulses in the rear track section 2T will occur at a time during which the track relay STR is not isolated from the rails of the track section 3T by the contacts |00 and |0| of relays 3C'I'P and SXCT, such inverse code pulses cannot cause its operation to opposite positions alternately since the inverse code pulses are always of the same polarity.

In brief, this form'of the invention provides, in addition tobroken-down joint protection by isolation of the trackjrelay from the driven code pulses in the track section next to the rear, broken-down joint protection for inverse code pulses by reason of the Afact that such inverse code pulses are o f one polarity and can only operate the' track relay to lone position, in which it will remain unless legitimate code pulses are received over its own track section. For these reasons, it is believed that this invention provides an automatic block signaling system whichemploys driven code pulses of altemate polarity with distinctive rates, together with inverse code pulses for approach lighting and the like, and which has adequate broken-down joint protection.

Having'thus described two specic embodiments of the present invention, it should be understood that 4these forms are selected to` facilitate in the description of the invention rather Vthan to limit the'number of forms which it may assume; and it is'to be further understood that various modiiications, adaptations and alterations may be apduring which the inverse code following track relay ZATR is restored by its local circuit to one of its positions. With this preferred arrangement of polarities, any stray potentialon the track rails of the track section 2T, whichis of a polarity capable of simulating inverse code pulses in the energization of the relay ZATR, will be of a polarity to change the flow of current throughthe. resistor 2R causingrestorati'on of the relay 2ATR to its other position. Y

inverse code pulse, will ybe in a` direction to neu;- tralize-for overpower the battery 2B,l' andrit hus plied to the specicrforms shown to meet the requirements of practicewithout in anymanner departing from invention. e

What I claim is:

l. Ina coded track circuitsignaling system for i railroads, a forward track section separated from a rear track section by 'insulated joints, a signal governing the passage of traflic from the rear track section into the forward track section, code transmitting means associated with said signal Afor applyingdistinctive code .pulses to said rear track section, a code following track` .relay normally connected across the rails of said forward track section, isolatingmeanseffective during the application of each .code pulse to the rear'track section by said code transmitting means foisdis` connecting said track relay from'lsaid, forward track section. and means acting in response to Athe intermittent operation of said track relay for Y governing the indications, ofV said signal and for 1 lrendering said isolating` means ineffective.

2. 4lin acoded track circuit signaling system for railroads having adjacenttrack sectionssepathespirit or `scope of the present l Y i 6. In acoded track circuit signaling s rated 'by insulated jcints, a signal for governing traffic from a rear track section into a forward track jsect'ion,1V acode receiving track relay asso` ciatedl with said forwardV VtrackKV section" and ,nor-Q mallyV connected thereto, 'decodingmeans cone trolled kby the intermittent operation of said track relay `for governing theY indications of said signal, a code transmittingmeans governed bysaid decodingmeans and actngto apply code pulses'of different selected rates to said rear track section, and means governed by'said code transmitting V means Yfor applying time spaced means and effective during theY application of each code pulse to isolate'said tracklrelay from saidA forward track section, vand thereby render it immune from code pulses from. said transmitting means in tlieevent said insulated joints should become broken down.

3. In a coded track circuit signaling system'vfor railroads having adjacent track sections separated by.I -insulated joints, code transmittingV means for applyingk code pulses to the, rear track Y section, a code following track relay having circuit connections to the track rails of the forward alma-12o ylo code pulses of different polarities to the rear'track section, Va

ypolar-responsive'code receiving trackrelay associated withthe forward track section, contact means for disconnectingY said track relay from the rails of its section only during the time the code pulses are applied to the rear track section, defk coding means governed by said track relay so as to be distinctively responsive to the different 'A code rates repeated by said track relay, means for controlling said code transmitting means by said decodingimeans soas to transmit different code'frates selected in'accordancerwith the code Vrate then ygoverning said decoding means, and

means. controlled by' said decoding meansfor directly connectingy said track relayiacross the Yrails of its section independently of said contact means.

In acoded track'circuit signaling system for railroads, a forward track section 'separated from ya rear track section by insulated joints, a signal governing the passage of traifrom the rear track sectionV into the forward track section', code track section, contact meansgoverned by saidv code transmitting means for opening said circuit connections for said track relay while an impulse Y is being applied tothe rear track section, where# l by said track relay may not be energized by the Ycode pulsesV aloneapplijed to the rear track section in the event said insulated joints should become 'broken doWiLV-.and 'means responsive to the intermittent energizaton of said track relay by'` other legitimate code pulses for rendering said contact'kmeans ineffective.

V4.`In a coded track circuit signaling system which driven codepulses are transmitted ineach of a successionof track sections separated by in-` sulated joints, code transmitting means associated with the leaving end 'of each section for Y.

applying code pulses to that section in accordance with Vtraffic conditions in the next adjacent section in advance, a code receiving track relay Y normally connected across theentering end of each track section, isolatingrmeans associated g with each track relay and YactingV to isolatethat trackrelay from itsv track sectiononly during the time when the associated codetransmitting Qmeans for the adjacent section next in therear is applying a code pulse to such rear section, and y means associated withveach track relay and re` sponsive to its intermittent operation for renderingsaid associated isolating means'ineifective,

yand therebyrender that track relay responsive to said code transmitting means for connecting saidY tracklrelay across the rails-.of its section only duringthe time spaces between Vthe code pulses appliedto the rear4 track section, and means fgov'- erned byVV said trackrrelay and rendered effective l onlyin response to codepulses in said forward .Vtracks'ection for connectingsaidV track relay to its track section independentlygof the voperation Y of said code Vtransmitting means.

A code pulses infitsftrack vsection independentlyof ,l

transmitting means associated with said signal forrapplying code pulses of .dierent polarities to said rear track section, said pulses being of relatively short duration and separated Vby time spaces, a code following track relay of thetwo-` position magnetic stick type associated with said f forward track section, circuit meansfor connect-f ing said track relay across4 the rails of its sec.-i tion, said circuit means including contactsgovf erned by .said code transmitting means and effective Vto complete said connection only during the time spaces between the impulses applied'to the rear'track section, decoding means distinctively controlled 'by the` operation of said track relay. to its oppositeV positions in accordancewith theV different rates of the code pulses in the'forward track'section for governing thek indications of said signal, said decoding means responding to each distinctive rate independently of the momentary disconnection of its associated track relay, and means controlled ybysaid decoding means f for maintaining said track relay connected to the rails ofI its section independently of said contacts when aV particular code rate is received by said track relay.

8; In a coded track circuit signaling system for railroads, a forward track section separated from a rear track section by insulated joints, a signal governing the passage of traffic rfrom the rearV track section into the forward track section, a

code following itrack relay of the two-position;`

magneticV stick vtype normally Vconnected across the rails of said forward track section, decoding meansgoverned bythe operation' of said track i relayalternately to opposite positions in accordance with different'codefrates yfor governing the indications of said signal,V Vcode transmitting means associated with said signal for'applying code pulses of-opposite polarities alternately to said rear section at different code rates as selected by said decodingv means, isolating means controlled'by saidcode'transmitting means for Y lisolating said track relayfrom its track section i during the application ofieach code pulse to' said rear track section,.and means vcontrolled by saidv decodingV means for "rendering said isolating means ineffective onlyV in response to the recepf tion of a particular code rate bysaidtrack relay.

n ,Y s A Y n ystem for?,Y railroads, a Y forwfgudV and] .a rear track YSection separated by insulated /jointsfcode' transmitting Y75 Y 9. Inga coded track circuit signalingsystem..

having a plurality ontrack sections separatedv u v Yfrom, each other by insulated joints,Y- coded'track lcircuit apparatusv associated with' each section Y 17= Y comprising drivenflcode transmitting 'meansv at the leaving end 'oithe ectionI fortransmitting driven" code pulses; o opposite I' polarities alternately at;different selectedfrates A.driven code receiving vmeans Y'at1thje yentering erjid, o'f ,the'trackl Settim 'd iStinCtii/ely responsive' toythe different rates' ,ofdrivenccda and acting tojselect the `rate oi the driven"code infjthe next adjacent track section,finverse cjode transmitting means asso-` ciated with sa'idlcode receivingv means for transmitting` an inversefcode pulse' of apredeterminedk polarity on each evenl numbered driven code pulse, inverse code receiving means at the leaving end of the section comprising a polarized relay of rails of said forward track section only while code pulses are being applied to the rear track section, means for actuating said code transmitting means at certain different code rates under diilerent traiTlc conditions, and means responsive to an intermittent energization of said track relay at a code rate different from said certain code rates for the rear track section for connecting said track relay to the forward track section independently of the operation of said code transmitting means.

411. In a coded track circuit signaling system for railroads having a. plurality of track sections separated by insulated joints, code transmitting means associated with each track section for applying driven code pulses to the exit end of the next track section in the rear at a caution or a clear code rate dependent upon traine conditions, a code following track relay for the entrance end of each track section normally connected to the track rails of that track section, isolating means governed by the associated code transmitting means for isolating the track relay of the corresponding track section while that transmitting means is acting to apply code pulses to the next track section in the rear, and relay means responsive to the intermittent operation of the track relay for a given track section only at a clear code rate for rendering the associated isolating means ineffective, said clear code rates for adjacent track sections being different, whereby the means isolating a track relay from the code pulses applied to the next track section in the rear cannot be rendered ineffective by the clear code rate for that rear track section.

12. In a coded track circuit for railroadsy a track battery, a limiting resistance. code transmitting means for pole-changing said tracksbattery in series with said limiting resistance across the track rails at one end of a track section to provide driven code pulses of alternate polarity, means associated with the other end of said track section and governed by said driven code pulses for transmitting inverse code pulses of a xed polarity during the intervals following the driven code pulses of one particular polarity, an inverse code following track relay of the twoposition magnetic stick type, and means gov- 18r erned by said code transmitting` means' for alter-j n atelyA connecting said track relay,to the` trackl sectionand across a selectedpart ofy saidliniit; ing resistance, `saidtrack relay being operated ,to oneposition by saidinversef code -p :ulses andfto thefother position by the voltage dropacross 'said selected part of the limiting.resistancelonlywhen said transmittingvmeans is operated to apply 'al I driven code pulse of said particular polarity'. Y 13.` Inv a coded track Acircuit signaling .system for railroads having a plurality of tracksections separated by insulated joints, code transmitting ineansfat one end of each track `section andincluding` intermittently operated coding contacts for applying code pulses of alternate polarityat the beginning and the end of each closing operation of` said coding contacts',y a` code following;L

track relay of` the magnetic stick type at-theoth'er end of each track section intermittently operated bysaid vdriven code pulses :of 'alternate polarityv and inversecode transmitting means for s'aid other end of each track section governed by said code following track relay and eiective to apply an inverse code pulse immediately following every other driven code pulse, said inverse code pulses being of a fixed polarity, whereby the code following track relay of a track section cannot be improperly operated by the inverse code pulses for the track section next in the rear in the event the insulated joints separating these track sections are broken down. Y

14. In a coded track circuit signaling system for railroads having a plurality of successive track sections each separated from the adjacent track sections by insulated joints, coded track circuit apparatus associated with each track section comprising driven code transmitting means associated with the leaving end oi'each track section for transmitting driven code pulses of opposite polarities alternately at different selected code rates, code receiving means at the entering end of each track section responsive only to the driven code pulses of opposite polarities alternately and distinctively controlled in :accordance with the rate of reception of such pulses for selecting the code rate to be transmitted in the next adjacent section to the rear, said means also being eifecl tive on alternate impulses for transmitting an inverse code pulse of a particular polarity during the succeeding time space, inverse code receiving means at the leaving end of each track section responsive to each inverse code pulse in that track section so as to be operated to one position and controlled by the succeeding driven code pulse so as to be operated to the opposite position, and means controlled by the driven code transmitting means associated with the leaving end of each track section-for disconnecting the code receiving means for the next adjacent track section in advance during the application of each driven code pulse to such leaving end of the track section unless legitimate code pulses are being received in said advance track section, whereby said code receiving means for any track section is immune to either driven or inverse code pulses applied to the track section in the rear even Y though the separating insulating joints should break down.

15. In a coded track circuit signaling system for a succession of track sections separated from each other by insulated joints, signals for governing traiiic in one direction through said section, one signal at the entrance to each track section, coded track circuit apparatus associated with each signal comprising driven code trans- Q mittingrmeans flor/applying time, spaced pulses of ,Qpposte Ipolaritijes alternately.l togtlhe track I sectionin therear,` of the :associated sgnaflga odegreceiving ,trackl relayv associated Withthe section Yin* advance off the. signal, decoding means VresIlOnSive to the operationof said ,track..,r e1`ay to itsoppositevpositionsVforcontrolling the indi'- cationsfofsad signal 3andv selectingthe rateA of code pulse'sapplied by theassociatedcode transassociatedwith each j track relayfand controlled therebyfso yas to transmit .an inverse code ,pulse 0f afpartular polarityrfollowing. the reception ofjevery other driven code pulselhaving'aparrticu'larjpolarity, anr'inverse,codereceiving track L5.

relay connectedacrossthe track rails of the rear. seti'onduring thetinre spaces between successive. impulses yand operated 'to one positions bythe receptionofvjan inverse code1pu1se; and: means for c'zauskirigi` saidV inverse code t track relay. tok be n 91;-, l2p

eratedjto thevopposite. position during the trans'- meansV for transmtting ,inverse code; pulsesgof particular polarityci'n each track section; c eTv Q mittin'g'dmeans, inversev code transmitting means 1:0',

mission of each; ,driven code.L pulse t. of `a;p 1ar ity.

opposite.tasadparticmar polarity.. l 16.11; a ycoded track. circuit signaling? sy inwhich driven codepulses of opposite pol'stes alternately are transmitted in eachtracksecton..

arating insulated joints break dowmand whereby Y said inverse code'puls'eszof onlya particulfau,w polare.

Yity cannot operate said code Areceiving'meami'td its opposite positions.` Y Y i Y f NE1L DBRESTON.; 

